Sound is a physical disturbance in the medium through which it propagates. For example, in air, sound consists of localized variations in pressure above and below normal atmospheric pressure. Accordingly, the vast majority of sound reproduction system s are comprised of electromagnetic transducers in which an electrical signal is transformed into a mechanical vibration which, in turn, is transformed into an acoustic signal. Sound reproduction systems typically include separate loudspeakers, each generating sound within a selected frequency range. For lower frequencies, i.e., frequencies below 300 Hz., loudspeakers are typically comprised of a diaphragm, most commonly, a relatively large cone, a support system in which the cone or other diaphragm is mounted and a driver which vibrates the cone in a desired fashion to produce sound waves are used. For higher frequencies, i.e., frequencies above 300 Hz., horn loudspeakers, which are characterized by a smaller cone or other type of driver and speaker walls, positioned forward of the cone, which follow a selected pattern are more common.
While sound reproduction systems have been the subject of numerous innovations over the years, pattern control of sound projection within a particular listening area has remained a problem. Effective pattern control is particularly problematic when the sound reproduction system is installed in a stadium or other large structure. While it would be very desirable to provide even sound levels throughout the stadium, various considerations has made such a goal quite difficult. One problem is the dramatic variation between the distance separating the closest and furthermost listeners from the stage. Specifically, while the closest listener may be just a few meters from the stage, the furthermost listener may be as far as 300 meters away. Thus, sound reproduction systems suitable for use in stadium and other large venues must be capable of throwing sound considerable distances. As sound levels for high frequency sounds tend to drop off dramatically over distance, in order for high frequency sounds to travel these distances, the initial sound levels produced by the sound reproduction system must be quite high. For this reason, many sound reproduction systems capable of generating desired audible sound levels at the furthermost reaches of the stadium inadvertently produce sound far in excess of the desired audible sound levels close to the stage.
A common sound reproduction system used in stadiums and other large venues is generally referred to as a cluster system. Cluster systems are generally characterized by high efficiency, middle and high frequency range speakers having sharp vertical and horizontal directivity and high-power low frequency range speakers. In a cluster system, speakers are concentrated in one or two locations within the stadium or other large venue. While the location of a cluster system within a stadium or other large venue will vary depending on the particular uses contemplated therefor, in order for the cluster system to throw sound the requisite distances, cluster systems are typically elevated on the order of about 20 to 30 feet above their surroundings.
The elevation of cluster systems causes other problems. One such problem is that much of the sound produced by the cluster system will miss those areas immediately in front of the cluster. More specifically, low frequency range sounds are generally omni-directional and can propagate into those areas immediately forward of the cluster systems. High frequency range sounds, however, are highly directionalized and tend to propagated away from the cluster system in defined "beams" of sound. As those areas which are in proximity to the cluster systems are outside of the beams of high frequency sounds propagating away from the elevated cluster system, high frequency sounds generated by elevated cluster systems typically miss a front portion of the listening area. The size of the missed front section tends to vary depending on elevation of the cluster, width of the beam and upward slope of the listening area.
To address this shortcoming, cluster systems will typically include one or more down-fill loudspeakers for directing high frequency range sounds to the front section of the listening area. Unlike the remainder of the cluster system, the down-fill loudspeakers are angled relative to the ground so that the beam is directed into the front section. While this approach is successful, it greatly complicates the task of elevating the cluster system. Specifically, rigging an elevated down-fill loudspeaker at a proper angle so that the sound beam generated thereby will be directed into the front section of the listening area is much more difficult a task than rigging the remainder of the cluster system. Other proposed solutions involve downwardly angling both the driver and horn relative to the surface plane such that the beam exits from a horn opening formed at least partially in a bottom side surface of the down-fill speaker. While such an approach makes it possible to position the down-fill speaker cabinet parallel to the surface plane, such loudspeakers have yet to be widely accepted by the industry. For example, tasks such as storage and transport are seen by many as more complicated if the loudspeaker has a horn opening which extends along two surfaces.